The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.
Metal powders having a specific particle size and morphology are required for direct (additive) manufacturing processes such as cold spray, electron (laser) beam melting or continuous direct powder rolling processes. For example, titanium/titanium alloy powder used in electron (laser) beam melting preferably has a particle size of less than 250 μm with a narrow particle size distribution range. The particles are also required to have a regular morphology, such as spherically or cylindrically shaped powder particles, in order to provide high flowability.
Existing commercial titanium/titanium alloy powder production processes include hydride-de-hydride (HDH), gas atomization (GA), plasma-rotating electrode and plasma atomization (PREP) processes. Each of these processes requires the production of a solid Ti or Ti alloy feedstock product, such as a wire, bar, rod or billet, which is subsequently processed using brittle fracture, atomization, arcing or the like to produce the powder.
In the hydride-de-hydride process, solid Ti or Ti alloy feedstock are processed to remove contaminants, hydrogenated to produce brittle material and then ground under argon in a vibratory ball mill. The resulting particles are angular and measure between 50 and 300 μm. This process is time consuming, can introduce contamination, and produces particles having a sharp angular shaped morphology which are not favourable for additive manufacturing processes. In contrast, fine powders produced by plasma-rotating electrode and plasma atomization or gas atomisation methods are spherically shaped, but are extremely expensive to produce compared to hydride-de-hydride processed metal or metal alloy powders due to the high temperatures used to atomize the metal in these processes. Significant metal loss can also result from such process conditions.
It would therefore be desirable to provide an alternate method of producing a powder, preferably a powder having a desired morphology and size, suitable for additive manufacturing applications.